I don't know the name for the inner membrane of legumes, but i bet you're right WW, there must be a name for it.

it is a thin membrane, like the membrane between onion rings.. and yes, it is shiny, much shiner, and brighter, than the outer shell (especially a peanut that has a dull shell)

peanut growers do have a web site.. (i forgot to write it down, but they have a big blitz of ads now in the subway)
they might know..

and as for spanish peanuts, peanuts are a native american food, but they were quickly adopted by both the spanish and the portugues. they grow well in hot dry climates. their seeds are stored underground, and protected from many preditors. they have a long shelf life, and are a good source of protein and fat.. they are flavorful, so they made a good food for ships, and for planting near ports in in other countries -- so they quickly spread round the world. spanish peanuts are just a variety that were popular with spanish saliors/plantation holders.

when the spanish first came to americas, peanuts, (unlike corn and beans) where only found in aztec/mayan cultures.
the spanish introduced them to caribian, and amerian south..as a cheap easy to grow food for slaves.
(work for peanuts) they were also introduced to africa for the same reason (to have a cheap, stable food to feed ship board slaves.) no sharp objects needed to open, good quality food, easy to grow..
they moved into china and less successfully, japan, from spanish and portugues trader too.


my other obsession